Fibrous products comprising fibers bonded with dextran xanthate



United States Patent FIBROUS PRODUCTS COMPRISING FIBERS BONDED WITH DEXTRAN XANTHATE Leo J. Novak, Dayton, Ohio, assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio No Drawing. Application August 18, 1954,

Serial No. 450,796

16 Claims. (Cl. 92-3) This invention relates in general to fibrous products and, in particular, to products formed from discontinuous or short fibers and in which the fibers are bonded together in a coherent structure without benefit of weaving, knitting or other conventional textile processing. More specifically, the invention is concerned with new and novel so-called non-woven fabrics.

It is known in the art to make fibrous products from mixtures of two types of short or discontinuous fibers one of which is rendered adhesive by heat or solvents so that, while those fibers are in the adhesive condition, and usually with the application of pressure, the adhesive and non-adhesive fibers are autogenously bonded together by adhesion of the adhesive fibers to the remaining fibers. Such fibrous products, in diverse forms, have found acceptance in the trade as insulation, for coat linings, and so on.

While the fabrics comprising the two types of autogenously bonded fibers and obtained by comrningling the two types of fibers, activating the one type to adhesive condition, and pressing the fibers together while the activated fibers are in the adhesive state, are generally less costly than fabrics obtained by subjecting masses of discontinuous fibers to conventional textile processing, including carding and/or combing, drafting, etc. to form a yarn and then weaving or knitting the spun yards, they do involve the production of the potentially adhesive fibers, usually from a thermoplastic fiber-forming material such as a synthetic resin. The production of the resin or other thermoplastic, fiber-forming material, shaping thereof into continuous filaments, and disruption of the filaments into fibers of the desired short length, are relatively costly steps all of which contribute to the expense of the fabric obtained and the ultimate cost to the consumer.

it is an object of this invention to provide fibrous products, particularly non-woven fabrics made of discontinuous or short fibers which are, in general, less expensive than available fibrous products of that type.

Another object is to provide fibrous products, particularly non-woven fabrics made of discontinuous or short fibers in which the fibers are bonded together by a relatively inexpensive bonding agent and which do not depend on the use of expensive resin or thermoplastic fibers for coherence and strength.

A further object is to provide new and novel bonding agent for the fibers of a non-woven fabric or the like which can be applied to the fibrous structure in aqueous medium and which sets to bind the fibers together on drying of the treated structure.

These and other objects of the invention which will become apparent hereinafter are accomplished by the use of dextran xanthate as binding agent for the discontinuous fibers.

Dextran is a high molecular weight polysaccharide comprising anhydroglucopyranosidic units joined by molecular structural repeating alpha-1,6 and non-alpha-1,6

2 linkages, at least 50% of the linkages being, apparently, of the 1,6 type.

The dextran xanthated to obtain the bonding agent for the fibers may be obtained in any suitable way. Usually, it is obtained by inoculating a sucrose-bearing nutrient medium with a culture of a dextran-producing strain of Leuconostoc mesenteroides or L. dextranicum, or the enzyme filtered from the culture, and holding the mass until the dextran is biosynthesized from the sucrose in maximum yield, after which the dextran is precipitated from the fermentate as by the addition of a water-miscible aliphatic alcohol or ketone. The native dextran thus obtained is, under normal conditions, characterized by a very high molecular weight, calculated to be in the millions. It may be used as such in the Xanthation reaction, after suitable purification, reduction to particulate condition, and conversion to alkali dextran, or it may be partially hydrolyzed in any suitable way to dextran of lower molecular weight prior to being xanthated. In general, the dextran xanthated to obtain the bonding agent may have a molecular weight of 5000 to x10 determined by light scattering measurements.

The xanthate is obtained by reacting on the alkali dextran with carbon disulfide, the alkali dextran being formed when the dextran is dissolved or dispersed in an aqueous alkaline solution, preferably aqueous sodium hydroxide. By appropriate selection and correlation of the reaction conditions, dextran xanthates containing an average of from less than 1.0 up to 3.0 xanthate groups per anhydroglucopyranosidic unit may be produced.

In accordance with one preferred method, the dextran Xanthates are produced by the addition of liquid CS2 to an aqueous slurry or solution of the alkali dextran, such as and preferably sodium dextran, at a temperature of about 20 C. to 25 C., and allowing the reaction to proceed at the controlled temperature or at room temperature while subjecting the reaction mass to continuous agitation.

The molar ratio of alkali dextran to CS2 may be between 1:3 and 12:1, the reaction time may be between 2 and 4 hours or even longer. The reaction results in the production of a rather viscous mass which may be precipitated in a water-miscible aliphatic alcohol to obtain the dextran xanthate in the form of granules which may be filtered and dried to obtain the dextran xanthate in the form of a white to light brown powder.

Introduction of the xanthate groups into the dextran molecule may or may not appreciably alter the solubility characteristics of the starting dextran. These characteristics vary depending on the microorganism used in the biosynthesis which evidently influences the structure of the dextran, i. e., the proportion of 1,6 linkages therein and the water-sensitivity thereof. Dextran which is inherently water-soluble even in the native, unhy-drolyzed state, such as the dextran obtained using the microorganisms (or their enzymes) bearing the following NRRL (Northern Regional Research Laboratory) designations; Leuconostoc mesenteroides B-S 12; L. m. B119; L. m. B4190 and L. m. 13-1146, may be readily soluble in water, after xanthation, at low degrees of substitution up to an average of about 1.0 to 1.5 xanthate groups per anhydroglucopyranosidic unit, at higher substitutions, are usually less soluble in water or water-insoluble but dispersible therein.

The xanthates of dextran which is, in native state, difiicultly soluble in water or substantially Water-insoluble under ordinary conditions, such as dextran obtained using the microorganisms (or their enzymes) bearing the NRRL classifications: Leuconostoc mesenteroides 13-523; L. m. 3-742; L. m. B-1 191; L. m. B1196; L. m. B1144; L. m. B-1208; L. m. B-1216; Streptobacterium dexlranicum B1254 andBetabacterium vermiforme B-1139 are also difiicultly water-soluble or substantially waterinsoluble but may be dissolved or dispersed in a ueous medium under special conditions. For example, xanthated L. m. 8-512 dextran is insoluble in water but soluble in aqueous alkaline solutions such as aqueous sodium hydroxide. Such solutions may be used to incorporate the xanthate with the fibrous product.

The following is illustrative of the production of a dextran xanthate for use as bonding agent for the fibers.

About 10 gms. of particulate B523 native (unhydrolyzed) dextran are slurried in 200 mls. of hot (60 C.) water. A solution of 2.0 gms. of sodium hydroxide in 10 mls. of water is added and the mass is heated with constant agitation for one hour. It is then cooled to 25 C. and 2.0 mls. of liquid carbon disulfide are added dropwise. The mass is agitated for 2 hours at room temperature and then poured into methanol. The granular precipitate is separated by filtration and dried in a vacuum oven for about 12 hours at 60 C. The dextran xanthate (about 95% yield) occurs as a light brown powder and has an average D. S. of about 0.5. It is soluble in 2% to 10% sodium hydroxide solution, insoluble in water, acetone, toluene, morpholine and chloroform.

The detxran xanthate, when wet, is characterized by pronounced adhesiveness and when associated with the fibers in solution or dispersion is deposited on the fiber surfaces as an adhesive glaze which, on drying, serves to cement the fibers together at their contiguous surfaces or points of contact in the product.

In making the fibrous products, according to one variant of the invention, the fibers are deposited in any suitable way, and preferably in non-parallelized condition, that is not oriented in the same direction, and in the form of a web, mat, or bat of desired thickness, the web or the like is treated with a solution or dispersion, preferably aqueous, of the dextran xanthate, and the treated product is dried, with or without pressing, to obtain a product in which the dextran xanthate remains bonded to the fibers to secure them in a coherent structure which has good strength. Re-wetting of the fibrous product increases the adhesion of the xanthate to the fibers, and thus paper products in accordance with the invention have good wet strength.

The fibers may be deposited by drawing them downwardly through a suitable chamber onto an endless travelling foraminous collection surface by suction applied below the surface, or by blowing them through a chamber onto the collecting surface. The resulting felt-like web or bat of fibers may be moved on the travelling surface from the zone of deposition to a zone in which they are sprayed or otherwise treated with the solution or dispersion of the dextran xanthate, and then to a drying zone in which they may be subjected to a current of hot air under pressure, or pressed between platens or the like heated to a temperature below that at which the fibers are damaged.

According to another embodiment, the fibrous products are made on paper-making equipment, which permits of obtaining products of indefinite length and varying width. The fibers and dextran xanthate are distributed in the Water in the beater, with or Without beating of the fibers depending on the type of fiber used, the suspension is laid down on the screen, and the product is then dried and, optionally, calendered.

Various types of fibers may be used in making the products and particularly natural fibers of textile-making, paper-making length, or of shorter length, including those of cotton, flax, jute and other vegetable fibers; wool, hair, silk and other animal fibers; asbestos, glass, mineral wool; also artificial fibers comprising cellulose, such as regenerated cellulose or cellulose hydrate of all kinds, cellulose derivatives such as the ester, the ethers, mixed cellulose ester-ethers, hydroxy-alkyl and carboxyalkyl ethers of cellulose, xanthates of the cellulose ethers, cellulose thiourethanes, cellulose-fatty acids, dex ra a dQ ethers, and other fibers which are not rendered adhesive by heat without damage to the fiber structure and therefore cannot be used in making fibrous products of the type under consideration except in combination with more expensive resin fibers. The products may be formed of fibers which are of shorter length than is normal for textile or paper-making. Thus, they may be formed of rayon waste or 'fiockwhich comprises extremely short fibers or fibrils. The fibers will usually not have a length greater than one-half inch.

Synthetic fibers which are thermoplastic are not required for activation to adhesive condition to bind the fibers of the product together However, there are instances in which it may be desirable to use such fibers alone or in combination with the natural or artificial nonthermoplastic fibers. The synthetic fibers, and also artificial fibers of the type of regenerated cellulose, are characterized by smooth surfaces and normally cannot be used in the manufacture of paper, using conventional paper-making equipment.

In making paper from the usual paper-making fibers, an aqueous suspension of the fibers is beaten in the paper beater and during such beating the fibers undergo fibrillation and when the suspension is laid down on the screen dependence is placed on interlocking of the fibrillae of contiguous fibers to hold the paper web together. The synthetic and artificial fibers having smooth surfaces do not fibrillate on beating and therefore do not tend to interlock when an aqueous suspension thereof is laid down on the paper-making screen, even after vigorous beating of the suspension. Those smooth-surfaced syn thetic and natural fibers may be used in making paper or paper-like products in the practice of this invention, by including the dextran xanthate in the suspension in the beater with sufficient stirring (no heating required) to distribute the xanthate through the mass and then depositing the suspension on the screen, or by stirring the fibers in the water, laying the suspension down on the screen, and then treating the deposited fibers with a solution or dispersion of the dextran xanthate, and processing the resulting web of adhered fibers in the usual way. Preferably, when paper-making equipment is used, the dextran xanthate is dispersed or dissolved in the water in the beater, before or after introduction of the fibers. If an alkaline condition exists in the heater, or even if it does not an alkali soluble dextran xanthate may be used, such as dextran xanthate derived from an alkali-soluble dextran of the L. 111. 13-523 type, and may be introduced in the form of an aqueous alkaline solution, such as a solution in aqueous sodium hydroxide. When dextran xanthate soluble in aqueous alkaline solution of a given alkali concentration is added to the water in the beater, the dilution may reduce the concentration of the alkali to a point at which the dextran xanthate is not soluble and precipitates on the surfaces of the fibers in the form of minute, discrete masses which form discrete bonds between the fibers on deposition of the suspension and drying of the web. Such products, in which the fibers are held by the discrete mass or particles of dextran xanthate are characterized by increased porosity as com pared to products comprising fibers the surfaces of which are more or less glazed or coated by the adhesive xanthate.

Any of the natural or artificial fibers mentioned herein may be used, and may be used when the products are formed on paper-making equipment. Synthetic fibers which may be used, particularly when the products are formed on paper-making apparatus, include those of nylon, Dacron, Dynel, Teflon, and fibers formed of various vinyl polymers and copolymers, including those of polysacrylonitrile and acrylonitrile copolymers.

The amount of dextran xanthate incorporated in the fibrous product may vary and may be as low as 1% and as high as 25%, or even higher and up to 40% or 50%, on the weight of the fibers, depending on the relative flexibility or stiffness desired in the fibrous product.

In general, these products in which the fibers are chemically bonded together by the dextran xanthate are characterized by good strength in all directions and sufiicient flexibility to enable them to be manipulated. They may comprise fibers pre-dyed to any shade of any color, or may be printed for decorative effects, and may be used for a variety of purposes such as non-woven interfacing, backing, lining, reinforcement or padding in the apparel, upholstery, and home-decorating fields. The products are light in weight, may be more or less porous, have a smooth surface, and do not tend to ravel.

The following examples are given to illustrate the invention, it being understood that these examples are not intended to be lirnitative.

Example I Staple regenerated cellulose fibers are mixed with water in the beater of a paper-making machine to obtain a suspension. Five percent (on the fiber weight) of Waterinsoluble dextran xanthate (derived from L. m. 13-523 dextran and having a D. S. of about 2.0 is mixed with the suspension, together with 0.5% of mono-palmitate as agent and the mixture is laid down on the paper-making screen to obtain a web of fibers adhesively bonded by the dextran xanthate. The web is passed through the machine in the usual way. The dried, calendered web has a smooth surface and good strength.

Example 11 Regenerated cellulose flock consisting of extremely short fibers or fibrils is blown into an enclosed chamber the bottom of which is formed by an endless travelling foraminous screen. The fibers are collected on the travelling screen in heterogeneous, random lay to a thickness of one inch, and are then carried on the screen under a sprayhead which projects an aqueous sodium hydroxide solution of the dextran xanthate of Example I downwardly against them. The impregnated layer of fibers is then carried on the screen through a zone in which air under pressure and heated to a temperature of 100 C. is blown against them. The product is thus dried, with compaction of the fibers by the force of the air impinging against them.

The water-insoluble dextran xanthates are preferred for most purposes, and may be applied in the form of aqueous dispersions or emulsions, in aqueous alkaline solution where appropriate, or in organic solvents such as formamide. In preparing the aqueous dispersions or emulsions, various dispersing or emulsifying aids may be employed such as triethanolamine oleate, morpholine stearate, polyoxyethylene glycol stearate, etc.

Since certain changes in carrying out the above process, and various modifications in the article which embody the invention may be made without departing from its scope, it is intended that all matter contained in the above description shall be interpreted as illustrative and that the invention is not to be limited except as defined in the appended claims.

What is claimed is:

1. A coherent fibrous structure comprising discontinuous fibers bonded together by dextran xanthate.

2. A coherent fibrous structure formed of discontinuous regenerated cellulose fibers bonded together by dextran xanthate.

3. A coherent fibrous structure formed of discontinuous fibers of regenerated cellulose of shorter than normal textile-making length and bonded together by dextran xanthate.

4. A paper product consisting of paper-making fibers bonded together by dextran xanthate.

5. A paper-like product consisting of discontinuous smooth-surfaced unbeaten fibers bonded together by dextran xanthate.

6. A paper-like product consisting of discontinuous unbeaten regenerated cellulose fibers bonded together by dextran xanthate.

7. The method of making coherent fibrous products without benefit of weaving, knitting or other conventional textile processing, which comprises assembling a mass of discontinuous fibers in the form of a web in which the fibers are disposed in random array, treating the web with a dispersion of dextran xanthate, and drying the treated web to obtain a product in which the fibers are bonded together at their points of contact by the dextran xanthate.

8. The method according to claim 7, characterized in that the fibers are regenerated cellulose fibers.

9. The method of making coherent fibrous products which comprises preparing an aqueous suspension of dis continuous fibers having dextran xanthate distributed therethrough, depositing the fibers from the suspension in the form of a web in which the fibers are adhesively anchored together by the dextran xanthate adhering to the surfaces thereof, and drying the web.

10. The method according to claim 9, characterized in that the fibers are regenerated cellulose fibers.

11. The method of making coherent fibrous products without benefit of weaving, knitting or other conventional textile processing which comprises assembling a mass of discontinuous fibers in the form of a'web in which the fibers are disposed in random array, treating the web with a dispersion of dextran xanthate, and drying and pressing the treated web to obtain a compacted product in which the fibers are bonded together by the dextran xanthate.

12. The method according to claim 11, characterized in that the fibers are regenerated cellulose fibers.

13. The method of making coherent fibrous products which comprises preparing an aqueous suspension of discontinuous fibers having dextran xanthate distributed therethrough, depositing the fibers from the suspension in the form of a web in which the fibers are adhesively anchored together by the dextran xanthate adhering to the surfaces thereof, and drying and pressing the web.

14. The method according toclaim 13, characterized in that the fibers are regenerated cellulose fibers.

15. A mass adapted to be formed into a coherent fibrous web and consisting essentially of an aqueous suspension of discontinuous fibers having water-insoluble dextran xanthate distributed therethrough.

16. A mass adapted to be formed into a coherent fibrous web and consisting essentially of an aqueous suspension of discontinuous regenerated cellulose fibers having water-insoluble dextran xanthate distributed therethrough.

References Cited in the file of this patent UNITED STATES PATENTS 1,870,259 McKee Aug. 9, 1932 2,056,294 Richter Oct. 6, 1936 2,357,962 Leeman et a1. Sept. 12, 1944 2,609,368 Gaver Sept. 2, 1952 2,626,214 Osborne Jan. 20, 1953 2,674,517 Deniston Apr. 6, 1954 FOREIGN PATENTS 517,397 Great Britain Jan. 29, 1940 

1. A COHERENT FIBROUS STRUCTURE COMPRISING DISCONTINUOUS FIBERS BONDED TOGETHER BY DEXTRAN XANTHATE. 